Vodafone, one of the world's largest mobile phone groups, has revealed the existence of secret wires that allow government agencies to listen to all conversations on its networks, saying they are widely used in some of the 29 countries in which it operates in Europe and beyond.

The company has broken its silence on government surveillance in order to push back against the increasingly widespread use of phone and broadband networks to spy on citizens, and will publish its first Law Enforcement Disclosure Report on Friday.

At 40,000 words, it is the most comprehensive survey yet of how governments monitor the conversations and whereabouts of their people.

The company said wires had been connected directly to its network and those of other telecoms groups, allowing agencies to listen to or record live conversations and, in certain cases, track the whereabouts of a customer. Privacy campaigners said the revelations were a "nightmare scenario" that confirmed their worst fears on the extent of snooping.

In Albania, Egypt, Hungary, India, Malta, Qatar, Romania, South Africa and Turkey, it is unlawful to disclose any information related to wiretapping or interception of the content of phone calls and messages including whether such capabilities exist.

"For governments to access phone calls at the flick of a switch is unprecedented and terrifying," said the Liberty director, Shami Chakrabarti. "[Edward] Snowden revealed the internet was already treated as fair game. Bluster that all is well is wearing pretty thin – our analogue laws need a digital overhaul."

In about six of the countries in which Vodafone operates, the law either obliges telecoms operators to install direct access pipes, or allows governments to do so. The company, which owns mobile and fixed broadband networks, including the former Cable & Wireless business, has not named the countries involved because certain regimes could retaliate by imprisoning its staff.